Add observability platform Ansible project

Deploys the Grafana stack (Prometheus/Alertmanager/Loki/Tempo/Grafana with
Alloy as collector) and the ELK stack (Filebeat/Logstash/Elasticsearch/
Kibana) via Docker Compose on a target host. External to the application
repo, pre-built by the mentor.

ansible/playbooks/elk-grafana.yml

@@ -0,0 +1,10 @@
+---
+- name: Deploy ELK and Grafana
+  hosts: observability
+  become: true
+  vars:
+    observability_stack: elk-grafana
+  roles:
+    - docker
+    - observability
+